(1) Field of the Invention
The present invention relates to an improved method for inhibiting psychrotrophic bacteria in raw milk. In particular the present invention relates to a method wherein a non-lactose fermenting lactobacillus which produces hydrogen peroxide at refrigeration temperatures is added to the milk.
(2) Prior Art
Gilliland et al, J. Dairy Sci. 66, 974-980 (1983) described the use of various strains of lactose fermenting lactobacilli which generate hydrogen peroxide and activates a thiocyanate lactoperoxidase system in raw milk to inhibit psychrotrophic bacteria at 5.degree. C. or 7.degree. C. either alone or with a sorbate. Four (4) day cell counts of non-lactobacilli (i.e. psychrotrophic bacteria) were reduced by the use of the lactobacilli, particularly in the presence of sorbate. Other related references are L. Bjorck et al, Applied Microbiology 30, 199-204 (1975); B. Reiter et al., J. of Food Protection, 47, 724-732 (1984); E. L. Thomas et al., Infection and Immunity, 20, 456-463 (1978); and M. D. Northolt, Neth. Milk Dairy J. 38, 135-150 (1984).
Cultures are sold commercially for use in raw milk for cheese making as described in a paper by Sellars, R. L. et al at the 7th Biennial Cheese Conference, held Aug. 26-28, 1986 at Utah State University. The problem is that there is a need for cultures for use in raw milk which may be exposed to higher temperatures in transit without generating lactic acid from lactose in the milk. It is also important to generate significant amounts of hydrogen peroxide at refrigeration temperatures in the milk.
U.S. Pat. No. 4,320,116 to Bjorck et al. describes the use of chemical additives in milk including lactoperoxidase, a peroxide salt and a thiocyanate salt. The problem is that the raw milk is considered to be legally adulterated for some applications such as bottled milk.
The prior art has needed a reliable non-chemical method of preserving raw milk. The bacterial methods of the prior art have not satisfied this need because of lactose fermentation by the lactobacillus and/or insufficient hydrogen peroxide production at refrigeration temperatures.